Southern Hemisphere atmospheric circulation: role of teleconnections, sea-surface temperatures, horizontal resolution, physical parametrizations and topography on the simulated climate in a global climate model

SAURRAL, RAMIRO; CAMILLONI, INÉS; AMBRIZZI, TERCIO

Noumea

Conferencia; 10th International Conference on the Southern Hemisphere Meteorology and Oceanography; 2012

American Meteorological Society

In this work, the atmospheric-only CAM3.1 global model is used to explore the role of different horizontal resolutions, physical parameterization schemes, sea surface temperature (SST) distributions and its ability to represent the main teleconnection patterns. . A control run spanning a 10-yr period and using observed monthly SST fields as boundary conditions is performed to determine the skill of the CAM3.1 to represent the present climate. Validation results show the same underestimation pattern as in the WCRP-CMIP3 GCMs. Ssince CAM3.1 is an atmospheric-only climate model, this result suggests that the representation of the oceanic component and its impact on the atmosphere is probably not forcing the errors in the estimation of precipitation but that the source of the underestimation should be look for in the atmosphere itself. Consequently, a series of simulations were performed to explore the role of the size of the grid mesh: varying it from T42 to T85. Additionally, a simulation was carried out removing the Andes Cordillera (which runs almost parallel to the coast, along the western edge of South America) to study to what extent the representation of this topographic barrier determines the horizontal moisture flux fields and their impacts on precipitation genesis. Comparisons among the different simulations indicate that both horizontal resolution and topography have an important role in the representation of the atmospheric circulation of the Southern Hemisphere and also on precipitation over the region, . It is also found that errors in precipitation fields can be largely solved by improving the convective scheme considered. Consequently, the results of the different simulations performed suggest that the misrepresentation of rainfall over southeastern South America is a thermodynamic- rather than a dynamic-related issue.